APPENDIX—GEOLOGICAL SURVEY. 
413 
ing on the Potsdam ; tlie St. Peters’ sandstone, about 80 or 100 
feet thick, resting on the lower magnesian ; and the blue lime¬ 
stone resting on the St. Peter’s. This is the geological order ; 
and the thickness of these strata when every bed is in its 
place, is from 800 to 900 feet. 
Now let us see what our facts prove. We have the blue 
limestone on the east side of the state as far north as Green 
Bay; on the west side as far as St. Paul, while within our lines 
(or the width of the lead district) it extends no further than 
town seven in Iowa county. Thus we see that the blue lime¬ 
stone extends north along the flanks of this elevation one 
hundred and twenty miles further than it does along the cen¬ 
ter. But let us put these facts in another form. At Green 
Bay we find the blue limestone about on a level with the 
water; near St. Paul it occupies about the same relative 
position to the Mississippi; but through Wood and Clark 
counties the azoic is in many places above where the blue 
limestone -would have been if there had been no elevation 
there. 
If now we draw a line on a horizontal plane from the water 
level at the Mississippi to the water level at Green Bay, we 
shall find at each end of the line there will be at least 800 
feet of sandstone and limestone between the ends of our line 
and the azoic formation below ; while through Wood and 
Clark comities the azoic will stand not less than 200 feet above 
the line. Now if we sink our line down to a horizontal plane 
with the azoic on each end of it, we shall find the height of 
our elevation above it in the above named counties to be not 
less than a thousand teet. Here one hundred and twenty-five 
miles to the north of the lead district, we find a continuation 
of the same north and south elevation, and gaining in height 
as we extend north. 
While on this trip, I made a hasty visit to Lake Superior by 
way of Duluth and Bayfield, to where this north and south 
elevation would intersect the lake. Beaching the shore at 
Ashland, I extended my observations south about twenty 
miles, near the west line of range four west. This is near our 
